The formation of a metal layer on a substrate by coating from an aqueous solution is well known. Such depositions are frequently terminated by simply removing the substrate from the coating solution and rinsing it in water. For most applications, this is adequate. However, in certain applications it is essential to precisely control the thickness of the coating, either as a final product or for further processing steps. The conventional procedure may not be satisfactory in such circumstances because of variations in the transit time from the coating solution to the rinsing solution. The problem of how to precisely control the thickness of such a coating without resorting to elaborate and/or expensive equipment has been solved in accordance with this invention.